1. Field of the Invention
The present invention relates to the enhancement of sailing vessel performance where shoal draft is required, and in general, and to ship anti-roll fins. Sailing vessel performance enhancement is accomplished by improving keel efficiency, by making the keel adjustable as wind and sea conditions change, and by providing for a high righting momentxe2x80x94with a low center of gravity and by providing for the generation of dynamic stability.
2. Prior Art
Presently, most shoal draft ballasted monohull sailing yachts that seek to improve on the efficiency of an ordinary low aspect ratio keel employ:
(a) a keel/centerboard combination,
(b) a keel that widens at the tip (a version of which was patented by Henry Scheel, U.S. Pat. No. 4,089,286), or
(c) a xe2x80x9cwingedxe2x80x9d keel similar to that employed on the 1983 America""s Cup Yacht AUSTRALIA II, and on other yachts subsequently. (A variation on this was patented by Leonard Greene, U.S. Pat. No. 4,686,923. Another variation, by Warwick Collins of England, uses tandem primary foils connected at their tips by a single quasi-delta shaped voluminous end plate. Some designers employ xe2x80x9cwingsxe2x80x9d or xe2x80x9cwingletsxe2x80x9d in combination with a ballast bulb at the tip of the keel.)
Solution (a) makes draft, aspect ratio, and lateral area variable, but the forward location of the lowered centerboard is less than optimum, and the cavity in the keel eliminates volume that could be used for ballast, and generates turbulence. Solution (b) lowers the center of gravity and may help to reduce tip vortices, but is only a marginal improvement over a more ordinary design. Solution (c) goes farther, but on either tack one of the winglets is doing most of the work while the other is along for the ride, creating unnecessary drag. The winglets are not adjustable, and therefore efficiency in deep water is less than optimum, and the winglets remain deployed and susceptible to damage in shallow areas.
In addition to these commonly employed shoal draft solutions, there are several patents that employ a hydrofoil at the bottom of a keel to achieve various effects. These include:
(d) U.S. Pat. No. 3,324,815 xe2x80x94Morales
(e) U.S. Pat. No. 4,686,922 xe2x80x94Burroughs
(f) U.S. Pat. No. 4,703,708 xe2x80x94Cohen
(g) German Pat. No. DE 3713176 A1xe2x80x94Victora
(h) PCT Pat. No. WO 88/09286 xe2x80x94Van Houdt
The keels described in patents (d) and (e) are not hydrodynamically clean enough to achieve good overall lift/drag ratios. The solution employed in patent (f) is not conducive to shoal draft, and its two parts work against one another where opposing leeway is concerned when the lower foil is positioned to resist heel, causing the hull and upper foil to see a greater angle of attack than is optimal.
Patent (g) is broad, apparently encompassing several ideas. FIGS. 17-21 of that patent depict a pair of winglets that can be rotated about a longitudinal axis. The winglets are symmetrically opposed about that axis, and posts are shown inside the winglets for the purpose of individually adjusting their angle of incidence. The drawings do not appear specific as to the mechanism. In every orientation, these winglets would be vulnerable to damage from grounding or likely to snag mooring lines, lobster pot tethers, or other immersed objects. These observations apply equally to patent (h), the application of which to a sailing vessel that regularly heels is dubious.
Various patents seek to use a hydrofoil to lift the hull out of the water, in whole or in part. While this may benefit some sailing vessels at high speed, the likely result at lower speed is an increase in overall drag. Furthermore, unless the vertical force is generated to leeward of the vessel""s center of gravity a loss of righting moment, and therefore an increase in heel and a decrease of projected sail area will result.
It is an object of this invention to provide an improved shoal draft keel for performance oriented monohull sailing yachts.
It is another object of this invention to provide a hydrodynamically clean design with low tip losses for a good overall lift/drag ratio while providing adjustability to suit a variety of sailing conditions.
It is yet another object of this invention to contribute to good static stability by having a low center of gravity, and (in the preferred embodiment) to generate righting moment dynamically when additional stability is required.
It is yet another object of this invention to provide for the protection of vulnerable parts when the vessel is entering or departing a harbor, negotiating a shoal, river, or canal, or in any situation in which a shoal draft configuration is desired, and to provide a design unlikely to sustain serious damage in a grounding regardles of its setting.
It is yet another object of this invention to provide an adjustable and effective fin stabilizer design for ships, submarines, motor yachts, and other motor vessels.
Additionally, it is an object of this invention to provide a mechanism for the adjustment of its movable parts which utilizes forces and geometry in an novel and elegant way (in the preferred embodiment).
The invention comprises a primary foil attached to the canoe body of a sailing vessel at the root, and to a ballast bulb of generally circular section at the tip. The after portion of the bulb comprises a rotatable hub from which a relatively high aspect secondary foil (or xe2x80x9cwingletxe2x80x9d) protrudes. In the event this design is employed as a fin stabilizer on a motor yacht, or in any event, the bulb need not carry or constitute ballast, and may be no more than a protrusion from the trailing edge of the primary foil. In the preferred embodiment, the secondary foil has an adjustable flap on its trailing edge, as depicted in FIGS. 1 and 3. Alternatively, a one piece secondary foil of controllable or fixed angle of attack may be mounted. The hub is comprised of two parts, allowing the secondary foil to kick up should it strike a submerged object. Together, the hub and secondary foil can be rotated about an axis corresponding to the centerline of the bulb.
The secondary foil reduces the vortex about the ballast bulb which is caused by the primary foil, and the ability to reposition the secondary foil about the hub axis allows its setting to be optimized for each tack, windspeed, and heel angle. For short tacking in deep water, the secondary foil can be oriented down, away from the vessel""s hull. On long tacks, the secondary foil can be adjusted to a true vertical position, compensating for the vessel""s heel. Should the windspeed increase to where additional stability is required, the secondary foil can be repositioned to where it is approximately horizontal and to windward, and its effective angle of attack can be made negative using the adjustable flap, creating a downward force. [note: the last sentence and the following paragraph are not applicable to all alternate embodiments].
The motive force for rotating the secondary foil and hub can be achieved in a novel way. If the shaft controlling the flap on the secondary foil (or controlling the entire secondary foil""s angle of attack in one alternate embodiment) is adjusted while the vessel is moving forward through the water with sufficient speed, and if the hub and secondary foil are able to rotate freely, the flap will act as a vane, with the miter gear to which it is attached seeking its original position on the rotated flap adjustment gear. The novelty lies in the fact that this action will stop when the secondary foil reaches a cant consistent with the rotation of the adjustment gear, the effect being that the secondary foil will xe2x80x9cswimxe2x80x9d to wherever the adjustment gear is set unless or until the rotation of the hub is locked.